Bottom Line:
The residual unablated tumor is usually depicted on contrast-enhanced multiphase helical computed tomography (CT) as a focal enhancing structure during the arterial and portal venous phases.Contrast-enhanced color Doppler and power Doppler ultrasonography (US) have also been used to detect residual tumors.Based on our experience and reports in the literature, we consider that contrast-enhanced gray-scale harmonic US constitutes a reliable alternative to contrast-enhanced multiphase CT for the early evaluation of the therapeutic response to RF ablation for liver cancer.

ABSTRACTThe early assessment of the therapeutic response after percutaneous radiofrequency (RF) ablation is important, in order to correctly decide whether further treatment is necessary. The residual unablated tumor is usually depicted on contrast-enhanced multiphase helical computed tomography (CT) as a focal enhancing structure during the arterial and portal venous phases. Contrast-enhanced color Doppler and power Doppler ultrasonography (US) have also been used to detect residual tumors. Contrast-enhanced gray-scale US, using a harmonic technology which has recently been introduced, allows for the detection of residual tumors after ablation, without any of the blooming or motion artifacts usually seen on contrast-enhanced color or power Doppler US. Based on our experience and reports in the literature, we consider that contrast-enhanced gray-scale harmonic US constitutes a reliable alternative to contrast-enhanced multiphase CT for the early evaluation of the therapeutic response to RF ablation for liver cancer. This technique was also useful in targeting any residual unablated tumors encountered during additional ablation.

Figure 2: A 49-year-old-man with hepatocellular carcinoma before and after successful radiofrequency ablation.A. Contrast-enhanced CT obtained during the arterial phase before radiofrequency ablation shows a 2.0-cm hepatocellular carcinoma (arrows) with contrast enhancement in liver segment 8.B. Nonenhanced power Doppler US before radiofrequency ablation shows a few flow signals (arrowheads) in part of the hypoechoic tumor (arrows).C. Contrast-enhanced power Doppler US shows multiple flow signals (arrowheads) within the tumor.D. Contrast-enhanced CT obtained 20 minutes after radiofrequency ablation shows an ablation zone (arrows) of low attenuation, which represents the technical success of radiofrequency ablation. Note that the ablation zone is larger than the index tumor (i.e. the initially identified tumor prior to ablation).E. Nonenhanced power Doppler US performed 18 hours after radiofrequency ablation shows the hypoechoic ablation zone without flow signal.F. Contrast-enhanced power Doppler US again shows the ablation zone (arrows) without flow signal.G. On contrast-enhanced CT obtained 50 months after radiofrequency ablation, the ablation zone is no longer seen. The patient is still alive without recurrence.

Mentions:
During the first one year period (between April 1999 and March 2000), most patients treated with percutaneous RF ablation in our institution were evaluated with contrast-enhanced power Doppler US after RF ablation. These power Doppler US examinations were performed before and after the injection of a microbubble contrast agent, and the power Doppler US parameters were optimized. The color gain was dynamically adjusted to detect slow flows and to avoid noise. The pulse repetition frequency was maintained at 700 Hz. We started to scan with power Doppler US 20 seconds after initiation of the contrast agent injection, which was performed at a rate of 3 mL/min with an infusion pump (IPX4; IVAC Medical Systems, Hampshire, U.K.). We scanned intermittently to avoid early bubble destruction. With this technique, the enhancement effect lasted for more than 10 minutes. Focal areas with flow signals in the ablated lesions were considered as viable tumor portions (9). In our previous report involving the treatment of 73 hepatocellular carcinomas (HCCs) (12), contrast-enhanced power Doppler US showed no focal peripheral flow signals in 65 (89%) ablation zones (Fig. 2). In the remaining eight (11%) ablation zones, residual tumors were found on both the immediate follow-up CT and contrast-enhanced power Doppler US. The areas of the residual tumors on the power Doppler US were well correlated with the enhancing portions on CT (Fig. 3). Hence, 100% diagnostic agreement was achieved between the contrast-enhanced power Doppler US and immediate follow-up CT. Of the 65 ablation zones without residual unablated tumors, however, 10 (15%) had local tumor progression on follow-up CT.

Figure 2: A 49-year-old-man with hepatocellular carcinoma before and after successful radiofrequency ablation.A. Contrast-enhanced CT obtained during the arterial phase before radiofrequency ablation shows a 2.0-cm hepatocellular carcinoma (arrows) with contrast enhancement in liver segment 8.B. Nonenhanced power Doppler US before radiofrequency ablation shows a few flow signals (arrowheads) in part of the hypoechoic tumor (arrows).C. Contrast-enhanced power Doppler US shows multiple flow signals (arrowheads) within the tumor.D. Contrast-enhanced CT obtained 20 minutes after radiofrequency ablation shows an ablation zone (arrows) of low attenuation, which represents the technical success of radiofrequency ablation. Note that the ablation zone is larger than the index tumor (i.e. the initially identified tumor prior to ablation).E. Nonenhanced power Doppler US performed 18 hours after radiofrequency ablation shows the hypoechoic ablation zone without flow signal.F. Contrast-enhanced power Doppler US again shows the ablation zone (arrows) without flow signal.G. On contrast-enhanced CT obtained 50 months after radiofrequency ablation, the ablation zone is no longer seen. The patient is still alive without recurrence.

Mentions:
During the first one year period (between April 1999 and March 2000), most patients treated with percutaneous RF ablation in our institution were evaluated with contrast-enhanced power Doppler US after RF ablation. These power Doppler US examinations were performed before and after the injection of a microbubble contrast agent, and the power Doppler US parameters were optimized. The color gain was dynamically adjusted to detect slow flows and to avoid noise. The pulse repetition frequency was maintained at 700 Hz. We started to scan with power Doppler US 20 seconds after initiation of the contrast agent injection, which was performed at a rate of 3 mL/min with an infusion pump (IPX4; IVAC Medical Systems, Hampshire, U.K.). We scanned intermittently to avoid early bubble destruction. With this technique, the enhancement effect lasted for more than 10 minutes. Focal areas with flow signals in the ablated lesions were considered as viable tumor portions (9). In our previous report involving the treatment of 73 hepatocellular carcinomas (HCCs) (12), contrast-enhanced power Doppler US showed no focal peripheral flow signals in 65 (89%) ablation zones (Fig. 2). In the remaining eight (11%) ablation zones, residual tumors were found on both the immediate follow-up CT and contrast-enhanced power Doppler US. The areas of the residual tumors on the power Doppler US were well correlated with the enhancing portions on CT (Fig. 3). Hence, 100% diagnostic agreement was achieved between the contrast-enhanced power Doppler US and immediate follow-up CT. Of the 65 ablation zones without residual unablated tumors, however, 10 (15%) had local tumor progression on follow-up CT.

Bottom Line:
The residual unablated tumor is usually depicted on contrast-enhanced multiphase helical computed tomography (CT) as a focal enhancing structure during the arterial and portal venous phases.Contrast-enhanced color Doppler and power Doppler ultrasonography (US) have also been used to detect residual tumors.Based on our experience and reports in the literature, we consider that contrast-enhanced gray-scale harmonic US constitutes a reliable alternative to contrast-enhanced multiphase CT for the early evaluation of the therapeutic response to RF ablation for liver cancer.

ABSTRACTThe early assessment of the therapeutic response after percutaneous radiofrequency (RF) ablation is important, in order to correctly decide whether further treatment is necessary. The residual unablated tumor is usually depicted on contrast-enhanced multiphase helical computed tomography (CT) as a focal enhancing structure during the arterial and portal venous phases. Contrast-enhanced color Doppler and power Doppler ultrasonography (US) have also been used to detect residual tumors. Contrast-enhanced gray-scale US, using a harmonic technology which has recently been introduced, allows for the detection of residual tumors after ablation, without any of the blooming or motion artifacts usually seen on contrast-enhanced color or power Doppler US. Based on our experience and reports in the literature, we consider that contrast-enhanced gray-scale harmonic US constitutes a reliable alternative to contrast-enhanced multiphase CT for the early evaluation of the therapeutic response to RF ablation for liver cancer. This technique was also useful in targeting any residual unablated tumors encountered during additional ablation.